I. Field of the Invention
This invention relates to a cleaning apparatus as is commonly used in xerographic copying machines, and more particularly to a simple and inexpensive cleaning apparatus which removes magnetic toner particles from a moving surface within the machine by employing the combined effects of a mechanical scraping device and magnetic attraction.
II. Description of the Prior Art
In a typical xerographic process a photoconductor comprising a photoconductive composition coated on a rigid or flexible substrate is uniformly electrostatically charged in the dark, and then exposed by being illuminated in an image pattern in accordance with graphic material on an original document. The photoconductor becomes discharged in the areas exposed to the illumination, but retains its electrostatic charge in the dark areas, which areas correspond to the graphic material on the original document. The resulting electrostatic latent image is developed by depositing on the photoconductor a finely divided electrostatically attractable developing material (toner). The toner will normally be attracted to those areas on the photoconductor which retain a charge, thereby forming a toner image corresponding to the electrostatic latent image. This visible image of developing materials is then transferred to a support surface, such as plain paper or any other suitable substrate, to become the ultimate copy. Any residual developing material remaining on the photoconductor is removed therefrom by a cleaning device and the photoconductor is reused as described above for subsequent copies. The toner image that was transferred to the plain paper is then fixed thereto by either a heat or cold fusing process. If, for example, the developing material is heat fusible, application of sufficient heat to the paper causes the developing material to melt and be fused into the paper so as to be permanently affixed thereto.
It is during the transfer operation that it is desired to transfer all of the toner forming the image configuration to a suitable substrate, such as plain paper. However, it is fairly common during the transfer operation that toner particles remain on the surface from which the particles are transferred. If these toner particles were allowed to remain on, for example, the photoconductor surface, the particles would tend to accumulate and transfer to the next sheet of paper contacting the photoconductor, thus producing dirty copies. This process is commonly referred to in the printing art as "offset".
Various types of cleaning devices have been developed for copiers to avoid the above-identified problem and remove excess toner particles from a transfer surface. For example, the prior art discloses brush type cleaning devices which generally comprise one or more rotating brushes for removing the toner particles from a surface in combination with a flicker bar for cleaning the brush and a stream of air which carries the removed particles into a filtering system. Typical brush cleaning systems are illustrated in U.S. Pat. Nos. 3,278,932 and 3,483,679. The prior art also discloses various types of web cleaning devices which are typically fibrous webs that are moved relative to the surface to be cleaned and in contact therewith so as to remove the particles. See U.S. Pat. Nos. 3,186,838 and 3,615,397 for typical examples of this type of device. A third class of cleaning devices for copying machines are the blade type cleaning devices which generally include a flexible cleaning blade that is placed in contact with the surface to be cleaned so as to wipe the excess toner particles from the surface as the surface moves past the blade. Examples of this type of device are illustrated in U.S. Pat. Nos. 3,552,850, 3,660,863 and 3,871,762.
There are, however, various disadvantages in using each of the types of cleaning devices described above. For example, a cleaning apparatus such as the cleaning brush combined with an air flow and filter system require complicated and expensive apparatus which also tend to effect the reliability of the machine. Several of the known web cleaning devices are also complicated in structure, expensive and require constant maintenance. Furthermore, many of the web and blade cleaning devices cause abrasion of the sensitive surfaces being cleaned. Abrasion of the photoconductor's surface causes an immediate deterioration of copy quality. In addition, many of these systems often fail when a magnetic toner is used because of the strong bond of the magnetic toner particles to the surfaces which require cleaning.